Conversion of sodium sulfide to sodium sulfite



- June 1953- J. E. GREENAWALT CONVERSION OF SODIUM SULFIDE TO SODIUMSULF'ITE Filed May 26, 1948 ii 2 Sheets-Sheet 1 WN h INVENTOR. 0h; E,[lhlitalfld/b H TTORNE Y June 1953 J. E. GREENAWALT CONVERSION OF SODIUMSULFIDE TO SODIUM SULF'ITE Filed May 26, 1948 2 Sheets-Sheet 2 ,II, I

If TOKIV Y Patented June 16, i953 UNITED STATES PATENT OFFICE;

SODIUM SULEITE: J ,ohn E; Greenawalt, Bronxville, N. Y.Appljcation-;May-26, 1948, Serial No. 29,204- 15 Claims, (01. 23-1-1 29)Thisinvention relates to the production of the sulphites of alkalimetals-and more particularlyto conversion ofsodium sulphide (NazS). to.so.- dium sulphite (NazSOs).

Although there-are many recognizeduses for I sodium sulphite, one thatis particularly impor= tant isits use in the paper manufacturingindustry. In-this industry-theuse of. a cooking or digesting liquorcontaining sodium sulphite. or-amix-ture-oi sodium sulphite and sodiumbisulphite is known and is often preferred overthe. use of thecausticsodaprocess orv the sulphate process in which a mixture of caustic soda:and sodium sulphide are-the principal ingredients in the cooking liquor.By use ofthe sulphitecookling liquor, a greater yield of'pulp fibershaving superior'qualities is obtained than by. the use of theother'cooking'liquors mentioned. This. increased yield of superiorquality pulp may be as -much as 25% more'thancan be obtained by the useof either'the caustic sodap-rocess or the sulphate process in which amixture of caustic: soda and sodium sulphide. aretheprincipalingredients in the cooking liquor. This is believed to be due tothe-fact that sodium sulphiteis much milder in its action, and it'dissolves only relatively small portions of the valuable fibersorcellulose portion of the-wood, yet if properly ape. plied it is.sufiiciently strong. to act upon the incr-usting or non-celluloseportions of th wood to release-the fibers that are desired in the. pulp.Also,- this milder action of the sodiumsulphite on the wood in thedigesterspreserves the rfatu-.-.. rel-strength of the fibers to amuchgreater de gree than the more active agents, such as causticsoda andsodium sulphide. But, whateverhe the explanation, the use of sodiumsulphite in thepapermanufacturing industry would, Ibe-M lieve; be muchmore extensive becauseof the superior quality of pulp obtainable byitsuse but for the'fact that heretofore the known processes of producingor reclaiming the sodium sulphite-irom theresidual cooking liquor hasbeentooinefiicient' or high in cost to Warrant its use in manyinstances-whereit otherwise would be used;

It-is, therefore, an object of my invention to provide a process Ofproducing sodium sulphite in-a more direct and efiicient manner thanprocesses that have heretofore been suggested. or practised and also toprovide apparatus for carrying out my improved process. Division havingbeen required by the Patent Qfiice, the clairnsofthis application aredirected to-theprocess; lhe apparatus is claimed in applicants copendmgtrated and then burn It will beseen that with such a process the con-vversion from sodium su nhideto sodium sulphite involves the, formationof thiosulphate and then oxidi i th s. iosu pha e to. sod um u phiAccording to the present invention sodium sulph de m y be onvert d yirect i i n 0 sodium sulphite without the intermediate formationoflargeamou ts. f the thiosulp Th addition of water isnot necessary and nocaustic soda, is, formed or required and-at all stages of the treatmentonly a small portion of the material is. in thenfonnof'thiosulphate(NazSzOs). Consequently the conversion is practically all accomplishedbydirect oxidation of the sodium sulphide to sulphite according to thefollowing reaction:

cooking liquor. When wood chips, flax straw or other fiber produ ingmaterial is treated withsod lim sulphite, such as in the semi-chemicalprocess, it is desirable to reclaim or recover the spent sulphite orresulting sulphur compounds in a form for reuse. Heretoforaso far as Iam aware, there has been no practical and really commercially successfulmethod of reclaiming the spent cooking liquor so that it, can be reusedin the form of sodium sulphite. In some instances thepractice has beento waste thecooking liquor. This sometimes brings about a seri- *ousproblem of stream pollution. In some in stances the spent liquor hasbeen reclaimed as sodium sulphide and subsequently used in the kraft orsulphate process. But the drawback has been that there was no practicalmethod of converting the spent liquor back to a state in which it couldbe used in the form of sodium sulphite. Consequently, the use of sodiumsulphite in the paper and other industries has been hampered andlimited, notwithstanding its many desirable and well known qualities inthe manufacture of paper pulp or cellulose fiber materials. It is afurther object of my invention to overcome this drawback by providing aprocess of reclaiming the sulphur compoimds in spent cooking sulphiteliquor in a form in which the sulphur. compounds can be reused as sodiumsulphite.

According to one way of practising my invention the spent sulphitecooking liquor resulting from the production of pulp is concentrated byevaporating off enough water to put it in a state in which it can beburned. I Ordinarily the liquor is concentrated so as to contain 60% ormore of solids. The concentrated liquor is then burned in a suitablefurnace under reducing conditions to convert the sulphur compounds tothe corresponding sulphide. In this way, sodium sulphide in dry form isproduced from the spent cooking liquor. If too hot, it is first cooledand thereafter the sodium sulphide is treated in an oxidizingatmosphere, Without the addition of water, to convert the sulphide tosulphite.

According to' this manner of practising the process of the invention,concentrated spent sodium sulphite cooking liquor is burned in a furnaceunder a strong reducing atmosphere. This produces a residual molten massof sodium sulphide and other sodium compounds, especially sodiumcarbonate, which can be flowed from the furnace in a very hot moltenstate. Heretofore, it has been common practice to drop this molten massinto a tank of water Where it is dissolved to make an aqueous solution.With my process, this is not necessary. Instead, the molten masscontaining sodium sulphide and sodium carbonate is retained in dry solidstate and its temperature reduced. This reduction of the temperature ofthe molten mass should be carried out quickly. When it is sufficientlycooled it is then treated in dry state with air to oxidize the sodiumsulphide to sulphite. This is done by pulverizing the mass and treatingthe comminuted mass in an oxidizing atmosphere. This pulverizing may bedone in a ball mill, a

rod mill, hammer mill, disc grinder or other machine capable of finegrinding. The oxidizing is done with air and under controlledconditions. The oxidation may, if desired, be carried out with as littleas one or two percent of thiosulphate being formed while the amount ofsulphite produced may be as much as 50% to 60%, the balance beingsubstantially all sodium carbonate. A finished product may be producedin which about 90% of the sulphur compounds present is in the form of.sodium sulphite.

One of the difficulties encountered in the direct oxidation of sodiumsulphide is the tendency of the sulphide itself to burn or oxidize tothe sulphate form, the oxidation reaction being exothermic and sodiumsulphide is a highly combustible compound and may flash into flame at alow temperature. When this occurs the heat of combustion of theparticles is so great that oxidation proceeds to the sulphate form.Notwithstanding the low temperature of combustion of sodium sulphide, Ihave demonstrated 4 that if the exothermic heat due to the oxidation ofthe sodium sulphide is controlled according to my process, thetemperature of the material being treated can be as high as 250 C.without the formation of any material amount of sodium sulphate. Toobtain this desirable control, I prefer to use steam under pressure in ajacket about the zone or chamber in which the material is oxidizedinasmuch as a very close and fine control can be had in this manner. Byadjusting the jacketed steam pressure its temperature can becorrespondingly controlled. Hence, by maintaining the jacketed steam ata predetermined pressure the temperature can be maintained fixed so thatthe temperature of the material in the chamber, when the desiredoxidation is carried out, and the temperature of the air used for theoxidation can be nicely controlled; allowance being made for theexothermic heat of oxidation of the sulphide. Although I have mentionedjacketed steam under controlled pressure, under steam pressure may becirculated in the jacket as the water in a closed system under steampressure may be considered as having a temperature corresponding tosteam pressure.

The process may be carried out as a continuous one, the source materialcontaining the sodium sulphide being fed, pulverized, and thenprogressively oxidized and continuously discharged in the sulphite formfor reuse in the pulp cooking liquor or for such use as may be desired.

Although the novel features which are believed to be characteristic ofthe invention will be pointed out in the annexed claims, the in-'vention itself as to its objects and advantages and the manner in whichit may be carried out i may be better understood by reference to thefollowing description taken in connection with the accompanying drawingsforming a part hereof, in which:

Fig. 1 is a View in elevation, partly in section, of apparatus'embodyingmy invention;

Fig. 2 is a view on line 2-2 of Fig. 1; and

Fig. 3 is a view in cross-section, to larger scale, of the rod mill toillustrate the manner of pulverizing the material to be, oxidized.

The drawings illustrate an apparatus in which my process may be carriedout for converting sodium sulphide to sodium sulphite when the sourcematerial is the product recovered from the burning of concentratedresidual black liquor from the pulp digesters of a paper mill. It willbe understood that there are other sources of sodium sulphide and thatthe descriptionhere given is for purposes of illustrating one embodimentof my invention which may be used for carrying out my process when theproduct resulting from burning black liquor is discharged from thefurnace as a molten mass containing sodium sulphide and sodiumcarbonate. Such a furnace and a method of burning the black liquor isdisclosed in my copending application- In that apparatus the black 7Serial No. 641,995. liquor is burned in a reducing atmosphere and thesulphur compounds of the black liquor are recovered as sodium sulphidemixed with sodium carbonate. charged as a moltenflowing mass from adischarge spout which is illustrated in the drawings forming a part ofthis application and designated by reference number NJ; the furnacebeing shown conventionally by dotted lines.

Spout in leads into a cooling chamber H it will be understood that hotwater The product of the furnace is dis lI:ismroyidechmithi an. ntercamass where. e' heihotenass; disghareedi rom he isnon uieklyc oled."lhis: am er anseloneat rwate jacketed a. inner .wall fill 113 1911161"zfiQll fina lififlny monnted; wall stormin sa iacketedrspace i i htoieir nlate oo n k 14- .1s :nrovided: wit

Q i'flfl. .s lld- 5. 1 aava r .iil-z 3 1 .h, a. aolre edwcoclingchamber.ommunioa ngyr eiring1109x120; into;whichextendsya steamsiet nine :2 I:pro-vide zlavszith :a nozzle :22 -;positioned 3110 throwa;jet;of:steam;or waterziftdesi d, into,;the stream ;;,of-molten.:smelted produot'ziii vnowin from ;the -.sp.0,u.t :10. Thessteam:has .=:a idecided cooling 1 effect up.on 217118; molten amass which 1may hayesa;;temperature,- as ahighias @1690 slit; andxrdise integrates5113 gas it :falls 1 into i-the' :cooling tzoneill-fi of;cooling chamber1 l. a not courseeif .;water :;is' used .itziwiuibe-COI1VBI178d5tO steamibyathe heat; of thezhotsmelt. 'Thecoolingchamber is also provided witha rotatable screw conveyor :24. extending -;throughoutsitsilength.aItsshaft 25 ,iswmountedlto -rotate gin-bearings 52,6, andr21, mountedlonis'uitable frame (members :28 which are structural ,steel memberstied togetherto carry thesveightlof -the apparatus. The screwsconveyorjd is rotated bycmeans ofa prime-mover. -As sh0wn,;the e1cc,-tricemotorsBIl.isconnectedrto the-shaft byqardriving couplingsal;-:;Qommunicatingewith theinterior of cooling chamber H! atitsidi'scharge end is atdischarge:or;receiving:box;29. Thisibox conn'ects ;at .its :lower .end .';With';3tDp&I'.atllS to -.comminute; orgrind thecooled sodium sulphide product whichchas beenlbroken up during'its passage through :the. cooling -.zone 19 ;of the cooling. chamher.lI; .-This:box:29 serves-asatransfer chamber or conduit from sthecooling; chamber l to :the grinding apparatus. j w a v 'iC'onnecte'd to-'the;upper. end of lthe transfer box. 29- is. a conduiti30 :providedwith. an exhauster or 'blower 3| operated by aprime' :moverd'not shown):The lblowera=t3 l ,is commonly :fcalled an induced draftfan. Theconduit 30 ziszconnected to a dust vcollector :32 .which servesrto:separate thesconneotion substantially :air

has :a scolla-r; flrmto aWhiQh tithe ext-finder 2311-112X- tends. mzrApacking eland vthis 12111031. ded tozmak ight;

.,'; ZAS :slmwnjn higssthezinterior frtherrodrmill isprovidedwithiapnumher ofsspi alis pedzguide lea-files; 5.0 and {free stalling:reds. WI {thus when the rod mill is rotated in the directionofarrow521:.the irodscil. iserve ;=.t o @grindthe kenuppieces.nfssodiumxasulphide lproduct: grind ;it ;:is si nificant rte-motethat -as'zthis zmaterialsworks itsrsyay through theirodlmillit itsdischargesend th arsnm ressivapulverizingzof thepartieles which'l-providess: for progressively exnosinganew surfaces r of 113116:material, to sthe oxidizing v:air

which, last ;exn1ai-ned .hereinaften-Fis passed.throughcthemillrcountercurrentatothe passagesof Y the: charged:material.

rThesdischargeiendlofetherrod milliisiconnected t to a discharge-box;3swhichssenvesasiaitransfer chamber or conduit-d whichis .designatedgenerally lloy referenceznum eral 4-5. "This ;;stati.onary stra'nsfer:box; for ...the pulverized \material has la col1ari55 1 vawhich ex-'ferzboxs5-3 is provided .witheir conduit 15'!- for ;in-

particles oflsolid:prpductmvhich may be carried over from the apparatuslbyrthe airsstream which is mentioned hereinafter. a .2 y

' The broken .up .particles :of 1so'dium sulphide product are deliveredfrom the'coolingichamber l9 through zthextransfer. box 129 into the grindling apparatus-which inathisicase is arotatable rodmill 33. AlthoughI prefer .arod mill, :other types of comminuting :orgrindingzapparatus,

troducing air into ltheqjrodsmill to .pxidize t-he sodium-sulphide aslitisibeing KDI'QgYBSSiYBIyJDUIH verizedtandnas ritc-passes :through':ithe; rod .smill. An-Jair .lhefater 5.58 .rish-ownlconyentionally);is-.--pro-' vided to heat the air so that it cani-belintroduced intoethe grinding mill "under controlledxonditions 'of temperature. "Thelower aend'fof z'the transfer box 5.3 is :.connected;.-t.o the-oxidizingchamber 1254-; :It? is 2.2.18.0 provided with zaninlet 59 .which.isrconnectedsby' a conduitgfifl 'to theldust collector 32. so:thatwany; solidiparticlesrcollected, inxthe dustcollectormay bereturned-'tothesys tem and introduced :into "the oxidizing chamberv:material from :the rod.

jfltimayabe .n'oted.1here that :the air 54 along :with pulverized mill.133; stream from the;dustgcol1ectorr32. passes through a :discharge%conduit :fil eth-rough which it may .-be 7 passed to we scrubbers62(show-n .-conventionally-) to =recover any :fine :particles :of materialwhich mayfiescape ifro'mathe :dust. collector. Residual ainand gases lon t-then ibe passed l out ithrough a stack -(-not.shoWn).

The oxidizing chamberifitis ;-formed .by. an .elonate cylinderzfis-zwhich .is provided with a concentrically .mountedtcylinder r64sforminga jack- 1 eted, .space"z65..foratheicirculation of a-theatatranssuch asaball mill, hammer. mill, oridisc grinder; V

will suggest themselves in :the'light of the:-.-pres-j ent disclosure,it beingsignificant to note .that suitable means should :be provided to.finely -pulverize -the source material containing the :sodium sulphide.r n 1 :As shown the rod -.mi11 '33 comprises anv elongate rotatablecylinder 34 provided -:with insulation -35. It ismounted to rotate about:its axis" on a plurality ofsupporting rollers 36.1carried' onthestructural members-of the :frame. :At the inlet end the supportingrollers :36 ride in 3,.1'8-1 cessed ring-track 31 secured :to thecylinder 34 and atthe discharge end the rollers 36' engagea ring track-38. The rodmill is driven'bya prime mover. 1 As-shown, electric motor.39 (see Fig. '2).

gears. .gseeiflig. 19 flxedlto :thecylinderfit; :It will be noted :that:the transferi'box z-z9sroutlet end' fer medium :such :as :steam vor hotwater. :This steam sjacketed oxidizing chamber :54 is further insulated.by :a suitable insulating material 68.Thusfthereiisiprovidedanpxidizing chamber with a temperature..-controlling jacket. An inlet pi-pe 6:! into the jacketed space :65 isprovided with a :valve:68 andsanioutlet pipe 469 is provided withalcontrollvalve #10 soxthat the temperature,

,of ithe;ox'idizing chamber can be controlled by lthejacket-temperature, as desired. If Assumingi steam is-gbeing used lasaheat transfer" medium within ithe an acketed space 155,} its :tem-

controlling -pera ture can be nicely and closely controlled'gbyadjustment of the steam :pressure zasiindicated by :a gauge :11connected to the ;s,t'eam.;pressure system of the plantr it .b i sufiiie t o :note herezthatythe temperature of water and steam, in a' steam;boi er dollows ,or is a it m i n o th steam-pressure.

2 e id zi s ch mb -r 4 i n m ided with a rotatable screw conveyor 15,the tshaft lflii of sharewareiedKwrotate1msuitableear n nt o-;thevoxidizing chamber,

tendspverqthe. end.ofatheqcylinder;stand is pro:

11 and 18 supported in thef ra'me members- It is rotated by means of achain drive I9 connected to the driven shaft of motor 80, which isconnectedbycoupler SI-to'shaft 25. Consequently motor 88 drives'screwconveyor 26 in the cooling chamber I9 and screw conveyor 15 in theoxidizing chamber 54. 1

Connected to the discharge endof the oxidizing chamber is afinishedproduct receiving box 82 whichis provided with a discharge port 83. Thisis connected-to a discharge conduit 84 provided with a screw conveyor 85to carry the finished product to a suitable place for subsequent use.Also connected to the receiving box 82 is an air conduit 86 which isprovided with an air heater 8'! (shown conventionally) to heat the airso that it can be introduced into the oxidizing chamber 3 undercontrolled conditions of temperature and passedcountercurrent to thematerial beingtoxidized. Thus it will be noted that the apparatusprovides a temperature controlled oxidizing .chamber through whichpulverized sodium sulphide or other pulverized-material containingsodium sulphide may be passed and into which air under controlledconditions can be introduced and passed countercurre'nt to thepulverized material. It will be seen also that there is provided meansfor pulverizing the source material and means for cooling the sourcematerial.prior'to'comminution, all in a substantially closed systemunder controlled conditions of temperature. r 1

To illustrate my process for converting sodium sulphide to'sodiumsulphite, it may be described in connection with the accompanyingdrawings as appliedto the smelt from the concentrated cooking liquorirom.the semi-chemical .process or from. the-cooking liquor produced inthe sodium sulphite process in which thepredominating ingredient in theoriginal cooking liquor is sodium sulphite. In: either case, theresidual cooking liquor is concentrated, and burned in a reducingatmosphere. This produces a smelt containing the sulphur compounds inthe form of 7 sodium sulphide along with sodium carbonate. The smelt isproduced in molten state whichmay be flowed from the furnace (shownconventionally at through a discharge spout ID, some of the reducinggases from thefurnace 45 being drawn along through the spout; y .1

The hot molten smelt 23 containing sodium sulphide drops from thefurnacespout l0; into receiving box 20 where itencounters steam from thenozzle of jet 2!. Here the smelt is broken up, partly solidified andpartially cooled as it is blown by the steam into the cooling chamberIS. The charge is conveyed through this chamber and further broken up bythe screw conveyor 24. If a more intensified cooling of the moltenstream is desired, water or a mixture of water and steam may be jettedinto the molten smelt through jet v 2!. While the charge of material .ispassing through the chamber 19 it is subjected to the cooling action ofthewater cooled-walls of this chamber; the jacket I4 being cooled bycirculating water. v V Since the sodium sulphide is highly combustibleat high temperatures, it is protected until cooled to about 150 C. bynon-oxidizing gases drawn from the furnace Cooling water to control thetemperature of the cooling'chamber is introduced through pipe 15; passesthrough jacket I4, and is discharged through pipe '11. H J r rTheg'solid partially'cooled charge from cooling by the exhaust fan 3i.

chamber [9 is discharged into transfer box-29 and thence into rodmill 33where the material is crushed and progressively finely pulverized. Whilea rod mill is shown, the pulverizing step can be effected in any one ofnumerous machines designed for pulverizing, but I consider a rod millpreferable as considerable of the oxidizing of the sodium sulphide-canbe accomplished simultaneously' with the crushing. And, in this manner,the speed of oxidation can be reduced largely to the action on thesurface of the particles since the oxidation does not readily penetratethe surface of the particles, thus making it very difficult to oxidizethe interior of these solid particles. By continuously crushing theparticles, new surfaces are continuously-exposed to the oxidizing actionof the air current as the material slowly works its way through the rodmill. Air in desired amount and temperature is introduced throughconduit 51. and flows through the rod mill countercurrent to thematerial. By the time it reaches the fresh material coming fromthecooler 19 it is denuded of considerable oxygen and this furtherreduces the intensity of the oxidizing action when the material isricherin sodium sulphides I have found that it is the too rapid oxidation ofsodium sulphide particles that increases the temperature of theparticles beyond that of the predetermined temperature of the oxidizingapparatus and it is this increased temperature which should be avoidedbecause otherwise the oxidation will proceed to form unwanted sulphate.3 When the temperature of theparticlesreaches about 250C. the tendencyto form sulphate is noticeable-and the higher the temperature thegreater is the tendency to form sulphate. An

. to each other while they are undergoing theoxidizing process so as todisperse the heat created by the oxidation of the sulphide particles.This control of temperature and the other conditions is done bycontrolling the conditions of oxidation in the oxidation chamber 54.

As the partially oxidized pulverized material is discharged from the rodmill. 33 it. passes through transfer box 53 into the oxidation chamber54. .It is moved through this chamber by the screw conveyor 15,. whichkeeps the finely ground particles agitated. The temperature in thechamber is controlled by. controlling the temperature of they steampassing. through the jacket 65. The steam temperature is controlled bycontrolling its pressure. That is, it is possible tomaintain the desiredtemperature in the oxidizing chamber by maintaining a predeterminedsteam pressure, the temperature being varied as desired by varying thesteam pressure. I have obtained excellent results in an oxidizingchamber of this sort with a boiler pressure of 200 pounds (lbs. persquare inch) which maintained a temperature about 220 C. in theoxidizing chamber. The temperature of the air introduced into thischamber through conduit 86 should be at about 180 C. The temperature ofthe air can be maintained by passing it through the air heater 81 whichis heated with steam from. the plantv boiler. The oxidizing action 7may, in'some instances, be improved bymixing not harmful to: my process.

atr a-e30 a sm'a-llsamountz of' steam with the air. The action ofitherotating screw-conveyor. 15 slowly advances the material through thechamber 54- and at the same time-continuouslyexposesnew surfaces of thematerial to the oxidizing action of the heated air current passingcountercurrent toithematerial. The'temperature of themass of: pulverizedparticles undergoing oxidation should not substantiallyexceed' 250? 'C.and should. not be below about 160- C. For best re-. sults according: tomy present-experience; the temperature. in. the mass of particles in theX1 dizing: chamber should be at about 220 C.

.l'llhecsteamiffor maintaining the desired temperaturewithinztheoxidizing chamber 54 enters the jacket through the -pipe 61 and-passesout ofithetjacket with such water. as may condense. The air passesthrough .the chamber 54, then passes through the. box -3,.thence throughthe crushing. chamber orv rod mill 33 to. the. induced drafti fan 5. 3 lwhich blowsthe. residual products of :combustion [and fine. particleswhich-.may 'fl'o'attin it, .into.1the1d-ust collectorv 3-2. Particlescollected 1' in. .the dust collector. .are returned through conduit60 tothe mainstreamin box .53

for recovery;.. Residual air. and gasesfrom" the dust'collector are ledto the scrubber .62- and finally to the stack. The induced draft fan 3|alsoiiwithdraws"reducing gases from the furnace through; the spout Ill,through the cooling chamber l9,.. and; discharges these products alongwitlrttthe gas streamto. the collector 32 along witlnsuch. residual airas. results from the. introduction of gain. through. conduits.v 83. and.51. The treated or finished: material is discharged from the:oxidizing-chamber 154. into box .82; and thence through .dischargeconduit 84. Therecovered material.contains.sodiumsulphitetiwhichwaszinitially present. in. the charge as sodium sulphide and: also.sodium' carbonate-which was initially present; The recovered product maythen be dissolved in water and filtered. to make up sulphite cookingliquor for'the'pulp digesters. After use in the digesters, theiresidualcooking liquor. may then be recycled as describ'edabove, it-beingsignificant to note that there is no undue: accumulation of sodiumsulphate 'from--recycling because sodium sulphate isreduced: tosulphide'in the reducing furnace. Although the. smelt coming from thefurnace which makes upthe charge contains other -com"- pounds besidessodium sulphide, such as. sodium carbonate and possibly some carbon;theseare In fact' there is-" an advantage because they dilute thechargeso. that itis not sorich in sulphide and this aids-in the prevention-of-local heatof combustion or'oxidation from. forming too rapidly. Thecarbon; if present, iS alsohelpful in thepulverizing step because thesodium sulphidewill oxidize at-a temperature below the-ignition pointofcarbon; so that both the carbon and sodium carbonate presentp'assthrough the process-unaffected;

' f When my process isused as acyclic process,

the recovery: of chemicals will be veryhigh; run hing from to] but 'of'course-somelosses will occur in the: wash water and: other lossesfdueto'leaks-"and loss through furnace'ga'ses'jwilI occur:

These small lossesmust be replenished but-this may-be done yery'economically "accordingfto my process by adding saltcake; or'sodium"sulphate; to the reducing furnace charge" where itis reduced" to sodiumsulphide and. the sodium sulphide then convertedtosod'ium sulphite'by myI EXAMPLE I Accord-ingto;.one;.example of practising the processoflmyinvention, a charge containing35 of. commercia-L sodium-carbonateand 65% sodium sulphide-in moltentstate was cooled by subjecting itto. ajetrof steam in a cooling chamber, the-material was then crushed andpassed throughan. oxidizing chamber into which'a heated air current waspassed the temperatureof the mass:undergoingoXidation being. maintainedat about 220. C. The resulting treatedmaterial contained 71%sodiumsulphite (NazSQa), 5%v sodium sulphide (Nags), 1% sodiumthiosulphate (Nazszos), 3% sodium sulphate (Na2SO4-),- the balance;being sodium carbonate. Accordingly approximately 68% of the sodiumsulphide was converted to sulph'ite with Very little formation ofthiosul'phate and sulbhate. In the light of later experience it wasfoundthat crushing the material to greater fineness resultedinsubstantially higheryields'ofsulphite. I I

EXAMPLE-II In another example-,a charge-ofmolteni smelt ing-'cliamb'erto about C. It was'then ground in a disc'grin'der', through whichair was passed. The-materialdischarged from the disc grinder had a"flnenessanalysisapproximately as fol- "Ihetcrush'ednrat'er'ialwas thenpassed through the 'oxiclizin'gchamber countercurrent to the preheatedoxidizin'g air. which" was" introduced into the oxidizing chamber?The'teinperatureof the oxidizingfchamb'er"wascontrolled so that the massof pulverizedifcharge"was about 220 .C; 'The treated orffinishedproduct? discharged from the oxidizing; chamberfanalyzed" approximatelyas Thus it will be seen that my process is admirably suited tooonverting'the sulphur compounds in spent liquor from the pulp digesterinto sodium sulphite for making up sodium sulphite cooking liquor foruse or reuse in the pulp digesters.

EXAMPLE In In another instance a charge was treated to convert itssodium sulphide to sodium sulphite. This charge was the smelt fromareducing furnace wherein waste black liquor from a pulp digester wasburned. The molten charge was quickly cooled by a steam jet and passedthrough a cooling chamber to prevent oxidation until it had atemperature of about 150 C. The charge was ground to a fineness-of theorder mentioned in Example II. It was then passed through a steamjacketed oxidizing chamber through which preheated air was passedcountercurrent to the ground charge. The temperature in the oxidizingchamber was maintained at about 220 C. by controlling the pressure ofthe steam in the jacket around the oxidizing chamber.

The finished product was analyzed and found to be as follows:

Per cent Insoluble 1 Sodium sulphite (NazSO3) 2'? Sodium thiosulphate(Na2SzO3l 2 Sodium sulphide (NazS) 1 Sodium sulphate (Nazsoi) 3 Sodiumcarbonate (NazCoa) 63 It will be observed that of the sulphur compoundsin the finished product most of it is in the form of sodium sulphite,there being only 1% of sulphide left unconverted and only 2% and 3%respectively of thiosulphate and sulphate was present, the amount ofsodium sulphite being more than 80% of the sulphur compounds present.

From the foregoing disclosure it will be noted that my invention ischaracterized by a number of important and commercially advantageousfeatures. It provides a process by which sodium sulphide can beconverted to sodium sulphite by pulverizing solid sodium sulphide or asource material containing sodium sulphide and subjecting the pulverizedparticles to an oxidizing atmosphere at a temperature below that atwhich sodium sulphate would form in undue amount. The process may becarried out by direct oxidation of NazS to NazSOa without formation ofundue amounts of sodium thiosulphate in the finished product or as anintermediate reaction product. It provides a process by which largerparticles may be progressively reduced in size to expose new surfacesprogressively to the oxidation medium and thus better control of thetemperature conditions with prevention of flashing with its attendantgeneration of exothermic heat suificient to raise the temperature ofthe'mass to a point where sulphate is formed. The process may be carriedout as a continuous one and it will be noted it may be carried outadvantageously by a progressive and controlled oxidation process whereinthe material richest in sodium sulphide is progressively converted to 'amaterial richer in sodium sulphite bypassing the oxidizing air incountercurrent flow whereby the air becomes progressively poorer inoxygen and the material under treatment becomes progressively richer insodium sulphite.

Not only is my process adapted for use converting sodium sulphide fromvarious. SQUIQQ to 12 sodium sulphite but it is particularly suited to acyclic process in the paper manufacturing industry where it is desiredto use the sodium sulphite process because the sulphur compounds in thespent liquor can be reconverted to sulphite form for reuse over and overagain.

Moreover, a novel apparatus is provided for carrying out the processwherein the cooling. grinding and oxidation may be carried out as acontinuous process under controlled conditions, it being particularlysignificant to note that the temperature of the mass of charge can bepositively and nicely controlled by the use of a predetermined steampressure. This is particularly useful in a commercial plant because theplant steam boilers may conveniently, economically and advantageously beused in a simple manner to serve as a means for controlling thetemperature in the oxidation process.

The terms and expressions which have been employed herein are used asterms of description and not of limitation and there is no intention inthe use of such terms and expressions of excluding any equivalent of thefeatures shown and described or portions thereof, but'it is recognizedthat various modifications are possible within the scope of inventionclaimed.

What I claim is: v

1. A process of treating a charge containing sodium sulphide to convertthe sodium sulphide to sodium sulphite which comprises passing saidcharge in drystate through a pulverizing chamber, passing'air throughsaid chamber in contact with said charge, maintaining said charge dryandprogressively pulverizing and continuously agitating said charge insaid chamber thereby to expose fresh surfaces of sodium sulphide to theoxidizing action of said air while controlling the temperature in saidpulverizing chamber within predetermined limits, thereafter passing thepulverized dry particles of charge being treated through another chamberand continuously agitating said particles while passing air therethroughin intimate contact with said dry pulverized charge, and maintaining thetemperature in said other chamber at a temperature sufficiently high tooxidize thesodium sulphide to sodium sulphite but not high enough toform more than small amounts of sodium sulphate, thereby toconvert thesodium sulphide to sodium sulphite.

2. A process of treating a charge containing sodium sulphide to convertthe sodium sulphide to sodium sulphite which comprises passing saidchargein dry state through a pulverizing chamber, passing air throughsaid chamber incontact with said charge progressively pulverizing saidcharge in said chamber thereby to expose fresh surfaces; of sodiumsulphide to the oxidizing action of said air while controlling thetemperature in said pulverizing chamber within predetermined limits,thereafter passing the dry pulverized charge being treated throughanother chamber while passing air therethrough in intimate contact withsaid dry pulverized charge, and controlling the temperature in saidother chamber at a temperature sufiiciently high to oxidize the sodiumsulphide to sodium sulphite but not high enough to form more than smallamounts of sodium sulphate, thereby to convert the sodium sulphide tosodium sulphite, said-temperature control being effected by the use ofsteam the temperature of which is adjusted by adjustment of itspressure. 3. A process of treating a charge containing :acgasacsodium-sulphide to convert the sodium sulphide tosodium sulphite whichcomprisesgpassingsaid charge in dry state through a pulverizingchamber,passing air through said chamber in contact with said charge,progressivelyrpulverizing said charge in said chamber therebyto exposefresh surfaces of dry-sodium sulphide to the oxidizing :action of saidair while controllingthe temperature insaid pulverizing chamber withinpredetermined limits, thereafter-passing the dry pulverized chargebeing" treated through a jacketed chamber while passing air through saidjacketed "chamber in intimate -contact'-with "said dry pulverizedcharge, and maintaining-the temperature in said jacketed chamber at atemsulphide to sodium .-su1phite but notehigh-enough to form more thansmall amounts of; sodium perature sufliciently highito oxidize thesodium sulphate, thereby to convert the sodium sulphide 'tosodiumsulphite, the temperature insaid jacketed'ch'amber beingreffectedbypassing'steam *un'dencontrolled pressure through thejacket 4'. Amethodof treating" the sodium sulphide contained-in the .smelt from afurnacewherein :sul'phur: compounds-;';are converted to" sodium sulphideand thesmelt from the furnace-isidist- "charged as a molten masscontaining sodium sulphide and" other sodium compounds,includin'gsodium' carbonate which methodcomprises cooling the moltensmeltdischarged from the furna'ce' tO a temperature at which" itsolidifies,

thereafter pulverizing' the solidified product in dry' state, and?subjecting the dry pulverized product to an oxidizingatmo'sphere whileprogressively exposing :new surfaces "of-the dry'pul- :verized productto the oxidizing. atmosphere at I "T a temperature sufliciently high tooxidize the sodium sulphide to sodium sulp'hite but not higher than thatat which the-sodium sulphide would be oxidized to sodiumsulphate in more:than' negligible amounts.

' BIA: method of treating the sodium sulphide "contained in thesmeltfrom a furnace wherein sulphur compounds are converted "to sodiumsulphide and the smelt from the furnace is discharged asa molten masscontaining sodium sulphide and other sodium compounds; including sodiumca'rbonatewhich method comprises cooling the molten smelt dischargedfrom the furnace to a point where it solidifies bycontact 'ingthe moltensmelt with a jetof aqueous cooling medium, thereafter pulverizing'thesolidified product in dry state in-a-pulverizing chamber through whichair is passed in contact with the product tobe pulverized whileprogressively exposing new-surfacesofthedry-pulverized product to theoxidizing action of:the'air at a temperature sufiiciently high tooxidize, the sodium sulphide to sodium sulphite but not higher thanthat. at which the sodium sulphide would be oxidized to sodium sulphatein more than negligible amounts, thereafter passing the pulverizedparticles through an oxidizing chamber through which air is passed inintimate contact with said particles while maintaining the temperaturewithin said oxidizing chamber at a temperature sufiiciently high tooxidize the sodium sulphide but not higher than that at which the sodiumsulphide would be oxidized to sodium sulphate in more than negligibleamounts, thereof a pap'er miII which sulphur compounds as sodiumsulphide from I spent cooking liqu'o'r as asmelt from a reducingfurnace, addingsodium'sulphate tothe furnace to "increase the content ofsodium sulphide in the smelt drawnfrom the smelt while maintaining itunder condition to keep it dry;

tainin'g other sodiumfpu lverizingSaid charge which contains saidsodiverizing chamber in intimate contact with the charge andcountercurrent to the passage of the char'gewand becoming; progressivelypoorer in oxygen content while the charge introduced :into

said grinding'chamber and discharged from said oxidizing chamber becomesprogressively poorer in sodium sulphide and richer in sodium sulphite.

n7; Aimethod of: converting sodium sulphide contained ,in' a pulverizedcharge of-material foontaining'thesodium sulphide which comprisescontinuously passing the pulverized charge in dry stateithroug'hv achamber and passing a stream of'air through said chamber countercurrentto the passage'of said'charge while agitating the particles ofpulverized-charge inintimate contact with said moving stream of air, the7 method 'beingcarried out as a continuous process wherein thepulverized charge as it. passes through saidchamber is maintained underconditions effective to convert sodium sulphide to 'sodiumisulphite'a'ndthe stream of air becomes progressively poorer in'oxygen content and the3 charge: becomes progressively richer in sodium sulphite andprogressively poorer in sodium sulp'hide g 8: Amethod of producingsodium sulphite suitable for use in cooking liquor in' the digesterscomprises recovering the then pulverizing the dry smelt containingthesodium sulphideand subjecting the drypulverizedsmelt to an oxidizingatmosphere under" dry conditions effective to convert the sodiumsulp'hide in thedry smelt to sodium sulphite. I I I Aprocess'of"converting sodium sulphide to sodium sulphite in a'charge insolidified form concompounds which comprises um sulphide by grindingthesolidified chargein dry form, passing the pulverized dry charge througha reaction zone and simultaneously passing a current of air through saidreaction zone in by to convert substantially all of the sodium sulphidecontained in said smelt to sodium sulphite. c

6. A continuous process of converting the sodium sulphide contained in acharge to sodium intimate contact with the pulverized charge and insufiicient amount tooxidize said sodium sulphide to sodium sulphite,agitating said pulver- V ized charge while in said reaction zone therebysaid intimate contactbetween said current ofair and the pulverizedparticles of said to cause charge in said reaction zone, controlling thetem-' perature in said reaction zone at a temperature sufficiently highto oxidize said sodium sulphide to sodium sulphite but below 250 C.thereby producing a. pulverized product containing sodium sulphiteconverted from said sodium sulphide.

10. A process of converting sodium sulphide to furnace, cooling the aomesa sodium sulphite which comprises providinga solidified chargecontaining sodium sulphide and other sodium compounds in dry form.grindin said solidified charge to produce pulverized dry particleswithout previous addition of water, passing the dry pulverizedchargethrough a reaction zone while simultaneously passing a current ofair through said reaction zone in intimate contact with the pulverizedcharge and in' sufficient amount to oxidize said sodium sulphide tosodium sulphite, agitating said 'dry'pulverized charge in said reactionzone thereby to cause said intimate contact between said current of airand the pulverized particles of said charge in said reaction zone,controlling the temperature of the reaction zone within the range of160C.and 250 C. thereby producing a product'containing sodium sulphiteconverted from the sodium sulphide initially present in the charge andcontaining, if anyyno more than negligible quantities of sodiumthicsulphate and sodium sulphate.

11. A process of producing sodium sulphite from a dry charge containingsodium sulphide by converting the sodium sulphide to sodium sulphitewithout addition of water to th charge which. comprises establishing areaction zone, grinding the charge in-dry condition within said reactionzone to form dry pulverized particles containing the sodium sulphide;passing the pulverized'particles through said reaction zone whilesimultaneously passing a current of air through said reaction zonesuificient in amount to oxidize the sodium sulphide in the charge tosodium sulphite,

controlling the temperature in said reaction zone within the range of160 C. to 250 C.'Whi1e causing intimate contact between said particlesand said air, thereby converting said sodium sulphide to sodiumsulphite.

12. A process of converting sodium sulphide to sodium sulphite whichcomprises pulverizing a dry charge containing said sodiumsulphide to anextent that more than 30% of the pulverulent charge passes a 300 meshscreen and more than 85 passes a 200 mesh screen, passing saidpulverulent charge through an oxidizing chamber and simultaneouslypassing an oxidizing gas in intimate contact with the pulverulent chargein said oxidizing chamber, maintaining the temperature in said chamberabove 160 C. but not sub.- stantiaiiy higher than 250 C. and agitatingthe particles of the charge while in said chamber whereby to exposefresh surfaces of the particles containing the sodium sulphide to theaction of the said oxidizing gas thereby to produce sodium sulphite bydirect oxidation of the sodium sulphide.

13. A process of converting sodium sulphide to sodium sulphite whichcomprises passing a dry y 16 charge containing sodium sulphide in theform of pulverized particles through an oxidizin chamber, simultaneouslypassing a current of air through said chamber in intimate contact withsaid particles while maintaining the temperature within said chamberbetween 160 C. and 250 (3;, and agitating the particles in said chamberwhereby to continuously subject them to the oxidizing action of saidair, the temperature in said chamber being controlled by a steam heatedmedium out of contact with said particles, the term perature ofthe'ste'am heated medium being controlled-by adjusting the pressure ofthe steam.

14. A process of treating a fused charge containing sodium sulphide toconvert the sodium sulphide to sodium sulphite which comprisespulverizing'said charge in dry state, subjecting the particles of thepulverized charge in an oxidizing chamber in dry state to a current ofair while maintaining the temperature of the charge in said chamber atabout 220 C. and agitating the pulverized particles of the charge insaid chamber whereby to expose fresh surfaces of the particlescontaining sodium sulphide to the oxidizingaction of the air thereby toproduce sodium sulphite by direct oxidation of the sodium sulphide.

15. A method of treating a charge consistingof fusedpieces containingsodium sulphide to convert the sodium sulphide to sodium sulphite whichcomprises passing the solidified pieces into a pulverizing chamber,progressively pulverizingthe charge containing sodium sulphide in drystate in said pulverizing chamber, passing air through said chamber inintimate contact with said dry charge while maintaining the temperatureof the charge above 160 C. but below 250 C. thereby to oxidize thesodium sulphide-to sodium sulphite without forming more than smallamounts of sodium sulphate, the particles of charge being kept dry andbeing continuously agitated during the pulverizing of the charge wherebyfresh surfaces of sodium sulphide are continuously exposed to theoxidizing action of said air during the pulverizing of the charge.

JOHN E. GREENAWALT.

'Lunge: Sulfuric Acid and Alkali, Gurney and Jackson, 1909, vol. II,part II, page 858.

1. A PROCESS OF TREATING A CHARGE CONTAINING SODIUM SULPHIDE TO CONVERTTHE SODIM SULPHIDE TO SODIUM SULPHITE WHICH COMPRISES PASSING SAIDCHARGE IN DRY STATE THROUGH A PULVERIZING CHAMBER, PASSING AIR THROUGHSAID CHAMBER IN CONTACT WITH SAID CHARGE, MAINTAINING SAID CHARGE DRYAND PROGRESIVELY PULVERIZING AND CONTINUOUSLY AGITATING SAID CHARGE INSAID CHAMBER THEREBY TO EXPOSE FRESH SURFACES OF SODIUM SULPHIDE TO THEOXIDIZING ACTION OF SAID AIR WHILE CONTROLLING THE TEMPERATURE IN SAIDPULVERIZING CHAMBER THEREBY TO PREDETERMINED LIMITS, THEREAFTER PASSINGTHE PULVERIZED DRY PARTICLES WHILE PASSING AIR THERETHROUGH ANOTHERCHAMBER AND CONTINUOUSLY AGITATING SAID PARTICLES WHILE PASSING AIRTHERETHROUGH IN INTIMATE CONTACT WITH SAID DRY PULVERIZED CHARGE, ANDMAINTAINING THE TEMPERATURE IN SAID OTHER CHAMBER AT A TEMPERATURESUFFICIENTLY HIGH TO OXIDIZE THE SODIUM SULPHIDE TO SODIUM SULPHITE BUTNOT HIGH ENOUGH TO FORM MORE THAN SMALL AMOUNTS OF SODIUM SULPHATE,THEREBY TO CONVERT THE SODIUM SULPHIDE TO SODIUM SULPHITE.